Method for early warning chatter detection and asset protection management

ABSTRACT

The invention embodies the application of different combinations of the monitoring and data processing aspects as a means to develop an early warning chatter alarming system. Configuring an early warning chatter alarming system can be as simple as using nσ alarm settings to develop an alarming strategy from different trend conditions such as overall RMS, selected vibration frequencies, slope analysis, and wavelet analysis. A higher level of alarming is provided by using a time integrated approach to account for both intensity of the alarm variable and duration. Combining these different aspects with a predictive model incorporates process-operating conditions to enhance the alarming sensitivity for earlier detection and reduce false positives. Finally, combining the different alarming aspects with a rule-based decision making approach such as fuzzy logic allows alarming based on qualitative analysis of different data streams.

CROSS-REFERENCES

This application is a continuation of U.S. application Ser. No.13/277,545, filed Oct. 20, 2011, the contents of which are herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to methods, compositions, and apparatusesfor the detection and prevention of chatter in doctor blades on a Yankeedryer. As described at least in U.S. Pat. Nos. 7,691,236, 7,850,823,5,571,382, 5,187,219, 5,179,150, 5,123,152, 4,320,582, and 3,061,944, inthe tissue manufacturing process, a paper sheet is dried on a heateddrying cylinder, termed a Yankee or Yankee dryer. Often adhesivematerials are used to coat the Yankee surface in order to help the wetsheet adhere to the dryer. This improves heat transfer, allowing moreefficient drying of the sheet. Most importantly, these adhesives providethe required adhesion to give good creping of the dry sheet. Creping isthe process of impacting the sheet into a hard blade (called a doctorblade), thus compressing the sheet in the machine direction, creating afolded sheet structure. Creping breaks a large number of fiber-to-fiberbonds in the sheet, imparting the qualities of bulk, stretch,absorbency, and softness which are characteristic of tissue. The amountof adhesion provided by the coating adhesive plays a significant role inthe development of these tissue properties.

In addition, the present invention covers detection and prevention ofchatter in doctor blades used for cleaning residual coating from theYankee surface as well as the cut-off doctor blade used duringmaintenance operations on the creping doctor blade. The presentinvention focuses on the creping operation, but extension of methodologyto the cleaning and cut-off blade apply equally as well.

The Yankee coating also serves the purpose of protecting the Yankee andcreping blade surfaces from excessive wear. In this role, the coatingagents provide improved runabitity of the tissue machine. As crepingdoctor blades wear, they must be replaced with new ones. The process ofchanging blades represents a significant source of tissue machinedowntime, or lost production, as creped product cannot be produced whenthe blade is being changed. Release agents, typically hydrocarbon oils,are used in association with the coating polymers. These agents aid inthe uniform release of the tissue web at the creping blades, and alsolubricate and protect the blade from excessive wear.

Proper and sustained interaction between the Yankee coating and thecreping doctor blade is critical for both sheet property development andmachine runnability. In normal operations, the creping doctor blade tiprides in the coating on the dryer surface and experiences minimal out ofplane movement. However, if the amplitude of the out of plane movementbecomes high enough the creping doctor blade wilt oscillate above andbelow the sheet leading to the development of chatter that appears ascross directional (CD) defects. Sheet defects from chatter will appearas multiple holes in the CD or develop a lace appearance. Coatingdefects can exhibit long CD marks that are visible when viewed with astrobe light. Under severe chatter conditions, the doctor blade willpenetrate through the Yankee coating making direct contact with thedryer surface. If this occurs, potential damage to the dryer surfacewith the appearance of horizontal grooves on the metal surface canresult. Once the dryer surface becomes damaged, it can only be repairedby taking the machine out of production and regrinding the dryersurface. Regrinding is a costly operation, because of production lossesand cost of the procedure as well as degrading the dryer servicelifetime due to reduction in wall thickness that negatively affects thevessel pressure rating. Therefore, it is imperative for manufacturers toclosely monitor the process and identify when chatter is present.

Excessive vibration on the creping doctor blade, leading to chatterconditions, can originate through mechanical and operational or processconditions. Examples of mechanical vibration sources include pressrolls, pumps, felts, Yankee cylinder bearings, etc., as well as dryerroundness deformation caused by thermal non-uniformities. Once amechanical vibration source is identified, maintenance intervention tocorrect the problem often requires shutting down the equipment resultingin production loss. Conversely, operational practices or processconditions inducing excess vibration may include sheet moisture levels,coating chemistry, machine speed, basis weight, furnish, blade stick outand loading pressure, etc. can be attended to without interruptingproduction.

Regardless of the source, excess vibration experienced by the doctorblade can lead to chatter conditions affecting product quality, machinerunnability, and asset value. Operators will often rely on audible soundchanges or visual inspection (sheet quality or Yankee dryer surface) asthe first indication that chatter is present. However, this approach issubjective and not reliable often resulting in detecting chatter afterthe condition has become severe, thus making corrective action stepsmore difficult. To improve the reliability and detection sensitivity forchatter detection, condition monitoring (CM) technology usingpiezoelectric and/or microphone sensor(s) can be used. CM has a longhistory in the paper industry, but mainly for use in bearing monitoringon rotating components. Examples of using CM on the creping doctor bladeis limited and in these cases measurement analysis is made followingtraditional CM methods based on sensor signal level exceeding an alarmlimit. In this approach, the system state is assessed from the sensorsignal trend. A flat trend is considered a normal condition whereas anupward sloping trend indicates a wear condition, and a step change isconsidered a component failure. The dynamics of the Yankee dryeroperation can produce large variations in the sensor signal, withoutreaching a chatter condition. As a result, data analysis becomes morecomplex compared to conventional CM based on wear and failure detectionlevels.

Previous attempts to address this problem include: Aurelio Alessadriniand Piero Pagani, Chatter Marks: Origin, Evolution and Influence of theCreeping Doctors, Ind. Carta vol. 41, no. 4, June 2003, pp 120-129, S.Archer, V. Grigoriev, G. Furman, L. Bonday, and W. Su, Chatter and SoftTissue Production: Process Driven Mechanisms, Tissue World Americas,February-March 2009, pp 33-35, S. Zhang, J. Mathew, L. Ma, Y Sun, and A.Mathew, Statistical condition monitoring based on vibration signals,Proceedings VETOMAC-3 & ACISM-2004, pp. 1238-1243, New Delhi, India, MFugate, H Sohn, and C. Farrar, Vibration-based damage detection usingstatistical process control, Mechanical Systems and Signal Processing,Vol. 15, Issue 4, July 2001, pp 707-721, H Sohn, C. Farrar, Damagediagnosis using time series analysis of vibration signals, SmartMaterials and Structures, Vol 10, 2001, pp. 446-451, A. Heng, S. Zhang,A. Tan, and J Mathew, Rotating machinery prognostics: State of the art,challenges and opportunities, Mechanical Systems and Signal Processing,23, 2009, pp. 724-739, A, Messaoud, C. Weihs, and F. Hering, Detectionof chatter vibration in a drilling process using multivariate controlcharts,

Computational Statistics & Data Analysis, Vol. 52, 2008, 3208-3219, A.A., Junior, F. C. Lobato de Almeida, Automatic faults diagnosis byapplication of neural network system and condition-based monitoringusing vibration signals, Proceedings of the 2008 IAJC-IJME InternationalConference, ISBM 978-1-60643-379-9, and A. G. Rehorn, J. Jiang, P.Orban, State-of-the-art methods and results in tool conditionmonitoring: review, Int J. Adv. Manuf Technol, 26, 2005, pp. 693-710.Unfortunately to date none of these attempts satisfactorily address theproblems caused by chatter in doctor blades.

Thus there is clear need and utility for methods, compositions, andapparatuses for the detection and prevention of chatter in doctorblades. The art described in this section is not intended to constitutean admission that any patent, publication or other information referredto herein is “prior art” with respect to this invention, unlessspecifically designated as such. In addition, this section should not beconstrued to mean that a search has been made or that no other pertinentinformation as defined in 37 CFR .sctn.1.56(a) exists.

BRIEF SUMMARY OF THE INVENTION

At least one embodiment of the invention is directed towards a method ofdetecting and addressing chatter from Yankee dryer doctor blades used inthe creping process, cleaning, and/or cut-off operations. The methodcomprises the steps of:

over a period of time, with an sensor constructed and arranged tomeasure the frequencies and amplitudes of vibrations in a doctor bladeas it crepes a paper product, measuring the frequencies and amplitudesof the vibrations indexed by time,

collecting the measurements into a time waveform,

converting the waveform using a fast-Fourier transform having afrequency spectrum which includes distinct vibration bands,

correlating characteristics of the vibration bands with performanceproperties of the doctor blade and to define a baseline of acceptablevibration bands,

predicting from the correlated characteristics the degree of deviationfrom the baseline of acceptable vibration bands associated with doctorblade chatter, and

outputting when a data point on a vibration band exceeds the degree ofdeviation excessive chatter has occurred.

The sensor may be an accelerometer and/or a piezoelectric accelerometer.The measurements may be analyzed and modeled by a data processing deviceconstructed and arranged to utilize one process selected from the groupconsisting of: RMS data trending, neural network techniques, multipleregression analysis, AR, ARMAX, partial least squares, and anycombination thereof. At least one of the correlations may be determinedby comparing characteristics of the vibration bands with blade age. Themeasurements may be analyzed and modeled by a data processing deviceconstructed and arranged to utilize RMS data trending and where thedetermination is made at least in part by noting that the slope in a sawtooth shaped vibration band continuously increases over time with thesame blade and becomes discontinuous when the blade is changed.

The method may further comprise the step of defining a deviation fromthe baseline due to chatter to only occur when a deviation exceeds themean and standard deviation to of the baseline due to both an increasein magnitude and a duration of that increase greater than the meanduration of all data spikes in the waveform. The method may furthercomprise the steps of pre-determining the slope at which the blade istoo old to be desired for use and replacing the blade when such a slopemanifests on the waveform.

At least one of the correlations may be determined by comparingcharacteristics of the vibration bands with one factor selected from:track bearing, balance, dryer lubricity, dust levels, moisture levels,temperature, felt age, grade, furnish composition, coating chemistry,cleaning blade status (on or off), machine speed, external sourcevibrations, external pressure sources, and any combination thereof. Therange of characteristics of the vibration bands caused by the factor maybe so broad that the sensor must be capable of detecting frequencybandwidth spanning four orders of magnitude. In at least one embodimentthe sensor only indirectly measures vibrations of the doctor bladebecause it is engaged not to the blade itself but to a blade holderwhich is engaged to and provides more rigid support to the blade butwhich does not dampen the vibration to such an extent that an accuratemeasurement cannot be taken. The measurements may be taken synchronouslyand/or asynchronously. The output may be an alarm.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side view of an embodiment of the inventionutilizing an accelerometer sensor measuring the operation of a doctorblade.

FIG. 2 illustrates a perspective view of an embodiment of the inventionutilizing two accelerometer sensors to measure the operation of a doctorblade.

FIG. 3A is a graph of an RMS trend from an accelerometer utilizing theinvention.

FIG. 3B is a graph of an expanded view of an RMS trend from anaccelerometer utilizing the invention.

FIG. 4 is a graph of an RMS trend including an alarm set point from anaccelerometer utilizing the invention.

FIG. 5 is a graph of a time integrated alarm and accumulated alarm fromRMS data from an accelerometer utilizing the invention.

FIG. 6 is a graph of RMS residuals from a predictive model utilizingdata obtained from an accelerometer utilizing the invention.

FIGS. 7A-7C show a group of graphs showing the advantage of predictivemodeling for early warning chatter detection and to prevent falsepositive alarms.

FIG. 8 is a graph of estimated vibration frequency for different chattermark spacings on a Yankee dryer.

FIG. 9 is a trend graph of an integrated frequency band (15-20 kHz) withand without chatter visible in the coating.

FIG. 10A is the raw sensor data for one Yankee cylinder revolution froman accelerometer utilizing the invention.

FIG. 10B is a fast Fourier transformation (FFT) of the data in FIG. 10A.

FIG. 10C is a wavelet analysis of the recorded accelerometer timewaveform signal from FIG. 10A displayed as a scalogram plot.

FIG. 10D is an expanded view of the waveform from FIG. 10A showing onlythe zone from 0.225 to 0.272 seconds.

FIG. 10E is an expanded view of the scalogram plot in FIG. 10C showingonly the zone from 0.23 to 0.264 seconds.

FIG. 11 is a graph of slope analysis of RMS trend data.

DETAILED DESCRIPTION OF THE INVENTION

The following definitions are provided to determine how terms used inthis application, and in particular how the claims, are to be construed.The organization of the definitions is for convenience only and is notintended to limit any of the definitions to any particular category.

“Bevel” or “bevel surface” as used herein refers to the portion of theblade that forms the surface between the leading edge of the blade andthe trailing side of the blade and is typically the “working surface” ofthe blade.

“Bulk” means the inverse of the density of a tissue paper web and isusually expressed in units of cm.sup.3/g. It is another important partof real and perceived performance of tissue paper webs. Enhancements inbulk generally add to the clothlike, absorbent perception. A portion ofthe bulk of a tissue paper web is imparted by creping.

“Cross Machine Direction” or “CD” means the direction perpendicular tothe machine direction in the same plane of the fibrous structure and/orfibrous structure product comprising the fibrous structure.

“Doctor Blade” means a blade that is disposed adjacent to another pieceof equipment such that the doctor blade can help remove from that pieceof equipment a material that is disposed thereon. Doctor blades arecommonly used in many different industries for many different purposes,such as, for example, their use to help remove material from a piece ofequipment during a process. Examples of materials include, but are notlimited to, tissue webs, paper webs, glue, residual buildup, pitch, andcombinations thereof. Examples of equipment include, but are not limitedto, drums, plates, Yankee dryers, and rolls. Doctor blades are commonlyused in papermaking, nonwovens manufacture, the tobacco industry, and inprinting, coating and adhesives processes. In certain instances, doctorblades are referred to by names that reflect at least one of thepurposes for which the blade is being used.

“Fiber” means an elongate particulate having an apparent length greatlyexceeding its apparent width. More specifically, and as used herein,fiber refers to such fibers suitable for a papermaking process.

“Highly polished” means surface that has been processed by a sequentialprogression from relatively rough grit to fine grit with suitablelubrication and is highly planar and substantially free of defects. Suchsequential progression will be referred to herein as a “step polishingprocess.”

“Machine Direction” or “MD” means the direction parallel to the flow ofthe fibrous structure through the papermaking machine and/or productmanufacturing equipment.

“Paper product” means any formed, fibrous structure products,traditionally, but not necessarily, comprising cellulose fibers. In oneembodiment, the paper products of the present invention includetissue-towel paper products. Non-limiting examples of tissue-towel paperproducts include toweling, facial tissue, bath tissue, table napkins,and the like.

“Sheet control” as used herein, refers to the lack of vibrations,turbulence, edge flipping, flutter, or weaving of the web that result ina loss of control at higher speeds.

“Softness” means the tactile sensation perceived by the consumer ashe/she holds a particular product, rubs it across his/her skin, orcrumples it within his/her hand. This tactile sensation is provided by acombination of several physical properties. One of the most importantphysical properties related to softness is generally considered by thoseskilled in the art to be the stiffness of the paper web from which theproduct is made. Stiffness, in turn, is usually considered to bedirectly dependent on the strength of the web.

“Strength” means the ability of the product, and its constituent webs,to maintain physical integrity and to resist tearing, bursting, andshredding under use conditions.

“Tissue Paper Web”, “paper web”, “web”, “paper sheet”, “tissue paper”,“tissue product”, and “paper product” are all used interchangeably andmean sheets of paper made by a process comprising the steps of formingan aqueous, papermaking furnish, depositing this furnish on a foraminoussurface, such as a Fourdrinier wire, and removing a portion of the waterfrom the furnish (e.g., by gravity or vacuum-assisted drainage), formingan embryonic web, and in conventional tissue making processestransferring the embryonic web from the forming surface to a carrierfabric or felt, and then to the Yankee dryer, or directly to the Yankeedryer from the forming surface. Alternatively in TAD tissue makingprocesses, the embryonic web may be transferred to another fabric orsurface traveling at a lower speed than the forming surface. The web isthen transferred to a fabric upon which it is through air dried to adryness typically between 10 to 50%, and finally to a Yankee dryer forfinal drying and creping, after which it is wound upon a reel.

“Water Soluble” means materials that are soluble in water to at least3%, by weight, at 25 degrees C.

In the event that the above definitions or a description statedelsewhere in this application is inconsistent with a meaning (explicitor implicit) which is commonly used, in a dictionary, or stated in asource incorporated by reference into this application, the applicationand the claim terms in particular are understood to be construedaccording to the definition or description in this application, and notaccording to the common definition, dictionary definition, or thedefinition that was incorporated by reference. In light of the above, inthe event that a term can only be understood if it is construed by adictionary, if the term is defined by the Kirk-Othmer Encyclopedia ofChemical Technology, 5th Edition, (2005), (Published by Wiley, John &Sons, Inc.) this definition shall control how the term is to be definedin the claims.

In at least one embodiment of the invention, a method detects the onsetof creping doctor blade chatter. This method, by alerting machineoperators that blade chatter conditions are imminent, allows operatorsto take corrective action avoiding runnability problems and preventingdamage to the Yankee dryer surface. The method utilizes signal analysisusing at least one piezoelectric accelerometer operated near the doctorblade holder. In at least one embodiment the analysis method differsfrom conventional CM techniques by using a time-integrated approach. Asa first level approach, the signal is tracked based on both intensityabove an alarm limit and duration. This allows accounting for strongvibration, but short duration, as well as weaker vibration over longperiods. Enhanced monitoring is described by extending this method topredictive models using process input data, wavelet analysis forspatially resolved MD high vibration regions on the dryer surface, andtrend slope analysis to predict the onset of an encroaching alarmcondition. In all cases, the Yankee dryer exposure to excess vibrationis accounted for by tracking the accumulated time integrated value, thusproviding an historical record to help in maintenance scheduling.

In at least one embodiment the method comprises the steps of detectingdirectly or indirectly the vibration of the crepe doctor blade. In atleast one embodiment the sensor technology is robust enough to operatein harsh environmental conditions. The conditions include one or more ofhigh dust levels, high moisture levels and temperatures >125.degree.C.In addition, the geometric constraints around the creping operation mayrequire a compact sensor footprint. Furthermore, in some circumstancesthe sensor must be capable of detecting a frequency bandwidth spanningfour orders of magnitude (for example 10 Hz to 20 kHz).

In at least one embodiment the piezoelectric accelerometer used is atypical commercially available off-the-shelf sensor that meets thesecriteria. Industrial accelerometers such as the SKF model CM2207 arehermetically sealed and hardened with an acceptable footprint(54.times.30 mm) for mounting on or near the creping doctor bladeholder. In at least one embodiment the accelerometer is directly mountedon the crepe doctor blade to monitor the blade vibration as it is incontact with the coating and surface of the Yankee dryer. However,direct mounting on the doctor blade poses additional challenges withgreater geometric constraints, higher temperatures, and limited bladeservice life requiring frequent (a few hours to 24 hrs, depending on theprocess and blade composition) blade changes. Therefore, in at least oneembodiment the sensor mounting is positioned on the doctor blade holder.This provides an effective alternative since the blade holder is inclose proximity to and in contact with the doctor blade and is itselfstationary.

An illustration of one possible arrangement for mounting anaccelerometer on a doctor holder is shown in FIG. 1. In the bladeholder, the doctor back plate provides a flat rigid surface for sensormounting. In at least one embodiment the sensor mounting method is witha tapped hole on the doctor holder and thread fastener through thecenter of the accelerometer sensor. Adhesive mounting can also be usedbut at the sacrifice of higher frequency detection. Other blade holderdesigns used are the ladder back and super crepe as well as all othermeans known in the art and their equivalents. Regardless of the bladeholder design, sensor mounting close to the doctor blade on astructurally rigid support with minimum dampening is the preferredmethod. Sensor location along the doctor back CD is dependent on themachine operation. If possible, the sensor should be located inside thesheet edge and preferably, multiple sensors are used to monitordifferent zones in the CD.

Referring now to FIG. 2 there is shown an illustration of accelerometermounting inside of the sheet by the tending and drive sides on a Yankeedryer. In this case, sensors to mounted near the drive and tending sidesheet edge allow detecting differences in vibration frequencies andamplitudes between the sides. Therefore, using a minimum of two sensorspositioned equal distances from the tending and drive side edge is thepreferred approach. In principle, a single sensor could also be used,but at the sacrifice of sensitivity and monitoring the side-to-sidevariation.

In at least one embodiment signal transmission from the sensors mountednear the creping doctor blade is made through hard wire cable orwireless communication to a vibration data acquisition unit, e.g., theSKF IMX-S on-line multilog system or any equivalent thereof. Data sentby the sensor can be raw, e.g., waveform, or processed through amicroprocessor integrated into the sensor or signal transmission line.The data acquisition system processes the sensor data and displays theresults and alarm status as well as a providing a means to achieve andretrieve data. In at least one embodiment, the data acquisition systemcan monitor other process variables such as the machine speed and canuse a tachometer for synchronous data collection. Data collected fromthe acquisition system can also be routed through Ethernet or wirelessto a centralized location (within a corporation or external) where datafrom several monitoring systems can be further analyzed. Compiling thedata from several sites allows for the calculation of aggregateperformance properties and relative rankings of the blade chatterlevels.

Process variables for the Yankee dryer unit operation are dynamic withvarying time scales from minutes to days. Process variables such ascreping blade age, felt age, grade, furnish, coating chemistry, cleaningblade status (on or off), machine speed, etc., all contribute to thevibration signature observed on the creping doctor blade. In addition,vibration originating from other sources such as fan pump, Yankee dryerbearings, pressure roll, overhead crane, etc. can also propagate throughthe process structure to the crepe blade. The aggregate of the vibrationsources results in the overall vibration signature detected by thesensor. For a piezoelectric accelerometer sensor, the vibrationsignature monitored is a time waveform that can be collected synchronousor asynchronous relative to the Yankee dryer rotation. Taking afast-Fourier transform (FFT) of the waveform gives a frequency spectrumthat provides unique vibration frequencies and/or bands. Further datareduction is made by extracting the root-mean-square (RMS) from the FFTpower spectral density to get an overall and/or bandwidth vibrationmagnitude value to trend over time.

The RMS trend from an accelerometer mounted on the creping doctor bladeholder will show natural variations under normal operating conditionsbecause of the process dynamics. The complexity and multipleinteractions from the different vibration sources makes identifyingspecific process variables contributing to a unique vibration frequencyor band a difficult task. However, some general features such as bladeage are clearly observed in the RMS trend as a saw tooth pattern.Installing a new blade will reduce the RMS by improved efficiency(reduced drag) in cutting through the coating and removing the sheet. Asthe blade degrades over time, the drag will increase resulting in theRMS increasing. To illustrate this point, FIG. 3 shows an RMS trend for0-10 kHz bandwidth data collected over 11 days. The trend is composed ofa natural process variation baseline associated with the creping doctorblade age as well as periods where the RMS value spikes relative to thebaseline.

Different features on FIG. 3 are highlighted and a zoomed area shows theeffect of the creping blade age on the RMS trend (vertical markersindicate periods where a blade change occurred). Periods where the RMSlevels spike can potentially lead to degradation of the coating and/orthe dryer surface. The vibration source associated with these spikes isnot always obvious, and often requires further investigation of theprocess and operating (human and mechanical) conditions. Degradation ofthe Yankee coating or dryer surface may occur from a single RMS spikeevent or a cumulative effect over time. Therefore, minimizing thefrequency and amplitude of the RMS excursions above the natural baselineis a best practice scenario for maintaining runnability and assetprotection.

As a first level for chatter monitoring, the state of the creping doctorblade vibration is tracked by using an nσ alarm based on the mean andstandard deviation (σ) of RMS trend data that excludes the spikedperiods and no visible chatter is present in the coating or dryersurface. Alarming sensitivity is based on the user selected number ofstandard deviations from the mean. Alarming (real-time) is based on theRMS level or RMS level and time duration. For just RMS alarming, analarm signal (visual, audible or combination) is sent to the operatorand stored in a database when the RMS value is greater than the nσ alarmlevel setting. Different states of alarming can be selected by usingmultiple nσ settings. For example, a 2σ alarm level can be a warningalarm alerting the operator the RMS value is trending upward, but notyet reaching a critical state. If the RMS value continues to trendupward past the 3σ alarm setting then a critical alarm can be sent tothe operator. This method of alarming is commonly found in commercialcondition monitoring systems used in predictive maintenance on rotatingmachinery. In this application, condition monitoring tracks bearing,balance, and overall integrity health on machinery. As the bearing wearsthe RMS trend from a sensor (typically an accelerometer mounted near thebearing of the rotating shaft) will gradually increase indicating thatbearing maintenance such as replacement or lubrication is needed. Ifleft unattended the RMS level would remain at a high level or continueto climb upward.

Unlike traditional condition health monitoring, the dynamics of thecreping process can result in large RMS variations without developingchatter. Therefore, a transient RMS spike above an nσ alarm level doesnot necessarily warrant an alarm event. However, as the duration of theRMS value above the alarm setting increases, the probability ofdeveloping chatter increases. In this alarming mode, the alarm signalstrength (alarm*) is a function of both the RMS value>nσ alarm level(RMS⁺) and the duration the RMS⁺ signal remains above the alarm level.The expression for the alarm* signal is given by

Alarm*(RMS,t)=(w_(RMS)RMS⁺)(w,t)

where W_(RMS) and w_(t) are weighting parameters or functions, t is thetime above the alarm level, and RMS⁺ is the difference between the RMSsignal and the nσ alarm value. Trending the time integrated alarm signalwill show variations >0 for conditions when the RMS level is above thenσ set-point and increases with time. This method addresses both shortduration high RMS values as well as RMS values that remain slightlyhigher than the alarm level for long periods.

The second mode of alarming is based on the accumulative effect ofalarm* over time and can be trended continuously as well as reporteddaily, weekly, monthly, or yearly. The accumulated alarm*_(Acc) is givenby

Alarm*_(Acc)=Σ Log(Alarm*)

and represents the total excess vibration the Yankee dryer is exposed toover time. Minimizing the frequency, duration, and amplitude of thealarm*_(Acc) will reduce the Yankee exposure to critical vibrationlevels thereby minimizing maintenance and extending the asset servicelife. Trending the alarm*_(Acc) is useful for evaluating and predictingdifferent maintenance levels for the Yankee dryer ranging from simpleinspection to surface reconditioning. The accumulated alarm informationalso helps to identify differences in operating procedures, e.g.,between workers shifts, grades manufactured, furnish, etc., where thevibration levels may trend abnormally high.

An example using this alarming strategy for the RMS vibration datacollected over 11 days is shown in FIG. 4 for a 1.0 minute samplingrate. FIG. 4 shows the measured RMS data collected with a 3σ alarm leveldetermined from an independent training set of data. The plot shows thehistorical RMS trend recorded with the 3σ alarm level (dashed line).FIG. 5 shows the resulting time integrated alarm* value using unitweighting values. Under normal operating conditions alarm*=0.0, sincethe RMS value is below the 3σ alarm level. Also shown on FIG. 5 is theaccumulated alarm*_(Acc) value to track the total excess vibration thedryer surface has been exposed to over the 11 day period.

In at least one embodiment the alarming method also involves apredictive model that reduces or removes the process dynamicscontributing to the measured vibration. The benefit of using apredictive model is improved alarming sensitivity and reduction in falsepositive alarms. Numerous model building techniques such as neuralnetwork (NN), multiple regression, autoregressive (AR), autoregressivemoving average with exogenous terms (ARMAX), state-space, partial leastsquares, and any combination thereof, can be used to develop apredictive model based on the waveform, frequency spectrum, or RMS trenddata. Ideally, model construction begins by collecting process bumptesting data to develop cause-and-effect relationships. However, bumptesting is generally restricted to a limited range of process changes tominimize quality and production loses. To address this issue datacollection over long periods is required to capture process changes formodel tuning. Alternatively, continuous tuning (learning) using adaptivealgorithms can be used to update the model. Using a predictive modelrequires process input data that can be collected from the distributedcontrol system or monitored directly with the vibration data acquisitionsystem. In either case, the process data collected is used as a modelinput.

An example illustrating a predictive NN model of the RMS trend from FIG.4 based on a process model with 25 input variables is shown in FIG. 6 asa plot of the residuals (difference between the measured and predictedvalue). In this example, the creping blade age dependency is modeled byapplying a transformation on the blade change data that is reported asthe time of the event to force the model to have similar behavior. Thetransformation uses a fixed slope based on the average obtained from theRMS trend measurements over the life of a blade. Large residualsrepresent a process condition not captured by data in the model buildingstep. The large residuals may or may not be an actual chatter condition,but are an indication that excess vibration has propagated to thecreping doctor blade.

The advantages of using the predictive model for alarming is shown inFIG. 7A for time integrated alarming. FIGS. 7B and 7C show zoomed areasof FIG. 7A, illustrating two different cases. FIG. 7B shows a zoomedportion of the left hand side of FIG. 7A, and shows the predicted(residual) alarm* value appearing before the alarm* value from FIG. 4data. In this case, the predicted alarm* value occurs almost 60 minutesbefore the standard alarm* value. The early alarming results from lower3σ alarm level. FIG. 7C shows the right hand side of FIG. 7A, and showsjust the opposite effect with alarm* occurring first. In this case, theNN model accounts for the contribution to RMS from the processconditions and reduces or removes the occurrence of a false positivealarm condition.

In at least one embodiment of the invention, a vibration frequency orband is monitored with alarming based on simple nσ alarm level or timeintegrated alarming. Unlike many of the mechanical vibration sourcesthat occur at frequencies <500 Hz, chatter appears at higherfrequencies. In cases where chatter is visible in the coating or dryersurface an estimate of the frequency range is made by measuring thespacing between the chatter marks and knowing the dryer speed. As thechatter mark spacing decreases the chatter frequency increases as shownin FIG. 8 for a fixed 6000 FPM machine speed. Even at a chatter markspacing of 1 inch the estimated vibration frequency at this machinespeed is >1000 Hz. In the development of chatter by the stick-slipmechanism (S. Archer et. al., Tissue World Americas 2008) visiblechatter mark spacing is typically much less than an inch. Therefore,high frequency band monitoring can improve the measurement sensitivityto detect chatter. The sensitivity gain is obtained by focusing onsmaller spectral regions compared to monitoring the overall RMS that canbe affected by low frequency non-chatter events, e.g., the fan pump. Inaddition, changes in a narrow spectral region may be attenuated in theoverall RMS value because of averaging with the surrounding spectralfeatures.

Trend data shown in FIG. 9 highlights the difference in data observedfor the integrated frequency band (15-20 kHz) at conditions with andwithout chatter. The first section of FIG. 9 shows the integratedfrequency trend when no chatter is visibly observed in the coating ordryer surface. When visible chatter did occur in the coating, a stepchange in the integrated frequency resulted. Monitoring differentintegrated frequency bands is directly applicable with the simple nσ ortime integrated alarm* methods previously discussed.

In at least one embodiment of the invention, there is provided a meansto monitor and alarm the early onset of chatter through wavelet analysisof the time waveform. For synchronous data collection, the time waveformrepresents the vibration signal measured for one complete rotation ofthe Yankee dryer. Taking the continuous wavelet transformation (CWT) ofthe time waveform sensor data parses out the vibration intensity andfrequency information as a function of time. By knowing the Yankee dryerspeed and diameter, a transformation from the time to the MD spatialdomain is made. The MD vibration frequency and intensity is useful fortracking specific spatial zones to determine the onset of potentialchatter. For example, the MD can be divided into n number of zones totrend an averaged or cumulative vibration frequency, band, or local RMSvalue. Alarming using either the simple nσ or time integrated approachcan then be used to alert operators of potential problems. Inparticular, the wavelet technique will provide an early alarmingcondition for cases when chatter is initially developed locally beforethe formation of a chatter band around the dryer circumference.

An example of using the wavelet analysis on the time waveform vibrationsensor to data is shown in FIG. 10. The plot labeled FIG. 10A representsthe raw sensor data or waveform collected from a sensor mounted on thedoctor back as shown in FIG. 1. The data was collected over 0.64 secondsrepresenting one cylinder revolution. Spectral features and intensityfrom the FFT analysis (plot labeled FIG. 10B) is the integrated resultover 0.64 seconds, so the strong frequency bands observed near 7800 and11800 Hz represents the accumulated effect. Identifying unique spectralfeatures from the FFT is useful in data interpretation, but lackstemporal information. Wavelet analysis of the waveform addresses thisissue by extracting vibration frequency and intensity information atdifferent times. By applying wavelet analysis to the waveform, ascalogram plot is constructed (labeled FIG. 10C) to display the squaremagnitude of the complex wavelet coefficients from the CWT to displayfrequency and intensity as a function of time. Expanded views of thewaveform (labeled FIG. 10D) and scalogram (labeled FIG. 10E) illustrateclearly the correlation between the waveform features and spatialvibration frequencies. For example, in the zone between 0.234 and 0.236seconds an intense band of vibration frequencies >10 kHz is observed.This frequency band shows up sporadically throughout the scalogram, butat this particular time (location), the intensity is maximum indicatinglocalized intense high frequency vibration.

In at least one embodiment of the invention, there is a means to monitorthe onset of early chatter detection by slope analysis of the vibrationfrequency band or RMS trend. A characteristic feature for trend plots ofRMS or selected vibration frequency bands is the effect of the crepingdoctor blade age. A newly installed blade causes an initial decrease inthe RMS trend. As the blade ages and wears the trend signal willincrease over time. Tracking the characteristic features of the trendsuch as the slope and marginal slope (2.sup.nd derivative) areindicators of the process state used in assessing whether a potentialchatter condition is approaching. FIG. 11 shows variations in the RMStrend slope that occurs under “normal” conditions between doctor bladechanges. Cases where the RMS increases to higher level than the normalrunning baseline is often preceded by a sharp increase in the slope.Tracking the slope then provides a means of predicting whether the RMSvalue is moving toward a higher trajectory.

In at least one embodiment of the invention, the method comprises asimple alerting method based on the time integrated alarm* value thatcould be color coded or audible. Color coded alarming utilizes a set ofcolors to indicate the current alarming state, e.g., green for normaloperation, yellow for an approaching chatter condition, and red for thepresence of a potential critical chatter condition. In this case, thetime integrated chatter condition accounts for both low and high RMSvalues above the alarm level at long and short time durationsrespectively.

While this invention may be embodied in many different forms, there areshown in the drawings and described in detail herein specific preferredembodiments of the invention. The present disclosure is anexemplification of the principles of the invention and is not intendedto limit the invention to the particular embodiments illustrated. Allpatents, patent applications, scientific papers, and any otherreferenced materials mentioned herein are incorporated by reference intheir entirety. Furthermore, the invention encompasses any possiblecombination of some or all of the various embodiments described hereinand incorporated herein.

The above disclosure is intended to be illustrative and not exhaustive.This description will suggest many variations and alternatives to one ofordinary skill in this art. All these alternatives and variations areintended to be included within the scope of the claims where the term“comprising” means “including, but not limited to”. Those familiar withthe art may recognize other equivalents to the specific embodimentsdescribed herein which equivalents are also intended to be encompassedby the claims.

All ranges and parameters disclosed herein are understood to encompassany and all subranges subsumed therein, and every number between theendpoints. For example, a stated range of “1 to 10” should be consideredto include any and all subranges between (and inclusive of) the minimumvalue of 1 and the maximum value of 10; that is, all subranges beginningwith a minimum value of 1 or more, (e.g. 1 to 6.1), and ending with amaximum value of 10 or less, (e.g. 2.3 to 9.4, 3 to 8, 4 to 7), andfinally to each number 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 containedwithin the range.

This completes the description of the preferred and alternateembodiments of the invention. Those skilled in the art may recognizeother equivalents to the specific embodiment described herein whichequivalents are intended to be encompassed by the claims attachedhereto.

What is claimed is:
 1. A method of detecting and addressing chatter fromYankee dryer doctor blades used in the creping process, cleaning, orcut-off operations, the method comprising the steps of over a period oftime, with an sensor constructed and arranged to measure the frequenciesand amplitudes of vibrations in a doctor blade as it crepes a paperproduct, measuring the frequencies and amplitudes of the vibrationsindexed by time, collecting the measurements into a time waveform,converting the waveform into a fast-Fourier transform having a frequencyspectrum which includes distinct vibration bands, correlatingcharacteristics of the vibration bands with acceptable performanceproperties of the doctor blade and to define a baseline of acceptablevibration bands, predicting from the correlated characteristics thedegree of deviation from the baseline of acceptable vibration bandsassociated with doctor blade chatter, and outputting when a data pointon a vibration band exceeds the degree of deviation excessive chatterhas occurred.
 2. The method of claim 1 where the sensor is anaccelerometer.
 3. The method of claim 1 where the sensor is apiezoelectric accelerometer.
 4. The method of claim 1 where themeasurements are analyzed and modeled by a data processing deviceconstructed and arranged to utilize one process selected from the groupconsisting of: RMS data trending, neural network techniques, multipleregression analysis, AR, ARMAX, partial least squares, and anycombination thereof.
 5. The method of claim 1 where at least one of thecorrelations is determined by comparing characteristics of the vibrationbands with blade age.
 6. The method of claim 5 where the measurementsare analyzed and modeled by a data processing device constructed andarranged to utilize RMS data trending and where the determination ismade at least in part by noting that the slope in a saw tooth shapedvibration band continuously increases over time with the same blade andbecomes discontinuous when the blade is changed.
 7. The method of claim6 further comprising the step of defining a deviation from the baselinedue to chatter to only occur when a deviation exceeds the mean andstandard deviation of the baseline due to both an increase in magnitudeand a duration of that increase greater than the mean duration of alldata spikes in the waveform.
 8. The method of claim 6 further comprisingthe steps of pre-determining the slope at which the blade is too old tobe desired for use and replacing the blade when such a slope manifestson the waveform.
 9. The method of claim 1 where at least one of thecorrelations is determined by comparing characteristics of the vibrationbands with one factor selected from: track bearing, balance, dryerlubricity, dust levels, moisture levels, temperature, felt age, grade,furnish composition, coating chemistry, cleaning blade status (on oroff), machine speed, external source vibrations, external pressuresources, and any combination thereof.
 10. The method of claim 1 wherethe range of characteristics of the vibration bands caused by the factoris so broad that the sensor must be capable of detecting frequencybandwidth spanning four orders of magnitude.
 11. The method of claim 1where the sensor only indirectly measures vibrations of the doctor bladebecause it is engaged not to the blade itself but to a blade holderwhich is engaged to and provides more rigid support to the blade butwhich does not dampen the vibration to such an extent that an accuratemeasurement cannot be taken.
 12. The method of claim 1 where themeasurements are taken synchronously.
 13. The method of claim 1 wherethe measurements are taken asynchronously.
 14. The method of claim 1where the output is an alarm.